Many industrial water systems require precise chemical treatment for any one or combination of the following: maintaining superior energy transfer, reducing waste, protecting assets, and improving product quality. Precise chemical treatment can be administered to an industrial water system by monitoring characteristic variables such as, e.g., conductivity, pH, oxidation-reduction potential, microorganism concentration, alkalinity, and hardness.
Measured changes in any of these variables can provide input into controlling process operations. For example, a measured increase in conductivity of cooling water circulating in a cooling tower operation may trigger a blow down of the operation followed by addition of make-up water, thereby reducing the conductivity of the cooling water. Maintaining accurate, precise measurement of characteristic variables of an industrial water system, particularly a cooling water system, is key to its efficient treatment and operation.
For industrial water systems, more particularly cooling water systems, three issues are generally addressed by treatment operations: 1) Inhibition of scaling caused by mineral deposition, e.g., calcium carbonate and/or magnesium silicate; 2) Inhibition of fouling caused by deposition of suspended deposits caused by, e.g., corrosion; and 3) Inhibition of microbial contamination caused by, e.g., bacteria, algae, and/or fungi. Any of these conditions may cause deposits to form on wetted surfaces, particularly surfaces that are utilized in measurement of a parameter of the industrial water system. Deposition of any of these onto a measurement surface are of particular concern, as deposition can introduce measurement error (inaccuracy, imprecision, or both) caused by, e.g., delayed measurement response time, measurement drift (e.g., changing offset), or measurement instability.
Several sensor probe cleaning devices and methods are available. For example, ultrasonic cleaning techniques exist for liquid systems comprising dissolved gases. Mechanical wiping systems have been implemented in some applications. Air jet, water jet, and off-line chemical treatments have been used as well.